The fluorescent lamp is the most widely utilized light source in the world for general illumination, primarily because of its relatively low initial cost and its efficacy: i.e., its light output relative to its power input, usually expressed as lumens per watt (LPW). Nevertheless, for home use, the fluorescent lamp has not taken precedence over the incandescent lamp. Many reasons have been advanced for this lack of acceptance, among them the poor color rendition of some fluorescent lamps and their need for a ballast. However, one of the major disadvantages lies in the fact that a fluorescent lamp is a linear light source whereas an incandescent lamp can almost be considered a point source. The typical fluorescent lamp has a length of from 18" to 8' and is somewhat cumbersome to work with.
With the increasing cost of energy, attempts have been made to overcome the latter difficulty. One of these attempts has utilized a plurality of fluorsecent tubes having one or more smaller tubes connecting the ends of the fluorescent tubes to provide an arc path. Such lamps are shown in U.S. Pat. No. 3,501,662. Large "U" shaped lamps such as those shown in U.S. Pat. Nos. 3,602,755; and 2,401,228; and triple bend lamps such as shown in U.S. Pat. No. 4,347,460 exemplify other attempts.
Still other attempts are shown in U.S. Pat. Nos. 4,208,618; 4,191,907; and 4,524,301, filed Sept. 30, 1982 and assigned to the assignee of the instant invention.
Yet another version comprises a plurality of glass tubes arranged in an assembly with appropriate arc directing means and electrode location to form a continuous arc path (see FIG. 1). The assembly is hermetically sealed within an outer envelope which contains an arc generating and sustaining medium or atmosphere to which all of the glass tubes are permeable.
This latter lamp includes a dense arrangement of electrical lead-ins which attach to the electrodes and thus are subject, when the lamp is operating, to a potential difference between them. Since these electrical lead-ins are positioned in an arc sustaining atmosphere, as opposed to an arc inhibiting atmosphere such as air, or a vacuum, the possibility of unwanted arcing between the lead-ins exists.
Organic insulating materials such as silicones and fluoropolymers are ineffective because of their outgassing characteristics.
Inorganic electrically insulating coatings containing glass and/or ceramic ingredients are also undesirable because it is difficult to match the expansion properties of wires to those of the glass and ceramic coatings available. It is also difficult to eliminate all of the pores in the applied coating, thus allowing shorting of the discharge in the regions of the pores.
Further, lead-ins so coated lose flexibility, an important feature.